Any increased use of women as bombers may complicate efforts by Pakistani security forces to stem a spreading wave of Islamist suicide attacks because it is harder to spot and search burqa-clad attackers in conservative tribal society.

Saturday's bombing illustrated the resilient ability of militants to stage attacks despite army offensives against them.

The woman blew herself amid a crowd of men, women and children heading toward a food distribution center of the World Food Program in the Bajaur region on the Afghan border."